Ventilation of underground porosity storage reservoirs

ABSTRACT

An underground porosity reservoir includes substantially impermeable barriers and an aquiclude surrounding a volume of alluvial deposits for storing water within the pore spaces of the alluvial deposits. A conduit positioned below a surface layer of the reservoir includes an interior volume that communicates with the pore spaces of the alluvial deposits. An air vent connects the interior volume of the conduit with atmospheric air above the reservoir and allows air to pass to and from the pore spaces of the reservoir. Ventilation of the porosity reservoir provides pressure-relief during reservoir filling operations (when the incoming water would otherwise cause an increase in air pressure within the reservoir), and further provides a vacuum-break as water is extracted from the reservoir (i.e., air from the conduit enters the pore spaces as the water is extracted).

RELATED APPLICATIONS

This application claims priority from U.S. Provisional Application No. 60/847,143, filed Sep. 26, 2006, which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

This application relates generally to a method of ventilating an underground porosity reservoir, and more particularly to a method of providing pressure-relief as the reservoir is filled with water and a vacuum-break as water is extracted from the reservoir.

BACKGROUND OF THE INVENTION

It is becoming increasingly difficult, both in terms of cost and site availability, to construct conventional open reservoirs for the storage of water. Such reservoirs typically require the construction of a dam across a river, thereby flooding vast expanses of land upstream of the dam while severely curtailing the flow of water downstream from the dam. In light of the increasing value of water and the complexities of the various water laws across different jurisdictions, it is becoming prohibitively difficult to form an open reservoir in this manner.

A further disadvantage of open reservoirs is the high degree of evaporative losses experienced by such reservoirs due to the relatively large air/water interface. Specifically, in arid climates (such as those found in the Western United States), open reservoirs are subject to extremely large evaporative losses. Indeed, such evaporative losses are typically greatest where water is needed most.

Underground porosity reservoirs, such as those described in U.S. Pat. No. 6,840,710 titled UNDERGROUND ALLUVIAL WATER STORAGE RESERVOIR AND METHOD, filed on May 15, 2002 and issued on Jan. 11, 2005, and incorporated herein by reference, have been posited as an alternative to open reservoirs. Underground porosity reservoirs include a volume of porous material, such as natural alluvium, bounded by substantially impermeable walls to create an underground vessel capable of storing water. Underground reservoirs are not subject to evaporation losses and can potentially be used without the loss of surface use of the site.

Methods of operating an underground porosity reservoir are described in co-pending U.S. patent application Ser. No. 10/704,347, titled METHOD OF OPERATING A WATER STORAGE RESERVOIR HAVING POROSITY STORAGE, filed Nov. 7, 2003, which is incorporated herein by reference. Following initial steps of building the substantially impermeable walls and pumping entrapped water back to the surrounding groundwater system, the porosity storage reservoir is typically filled to capacity and then emptied to determine the net storage capacity of the reservoir. Filling the reservoir to capacity typically produces water levels within the reservoir that are higher than would otherwise occur naturally within the alluvium. Depending on the amount of fine-grained materials existing between the sand and gravel particles, several filling cycles may be required to flush out these relatively fine materials and thereby increase the net capacity of the porosity reservoir.

One method of filling a porosity reservoir includes forming vertical wells to allow water to be directly injected into the reservoir (either passively by gravity or by the application of pressure). One such method is described within U.S. Pat. No. 7,192,218, titled DIRECT RECHARGE INJECTION OF UNDERGROUND WATER RESERVOIRS, filed on Feb. 23, 2005 and issued on Mar. 20, 2007, which is incorporated herein by reference. Another method for filling a porosity reservoir includes forming surface ponds and/or recharge ditches along the surface of the reservoir to allow water to gravity drain downward through the porous materials. In lieu of recharge ditches, a French drain system may be buried below the topsoil of the porosity reservoir so that water may pass through the perforated pipes of the French drain system and infiltrate downward through the reservoir. This method of filling the reservoir is described in greater detail in U.S. Pat. No. 6,840,710, incorporated by reference above.

Regardless of whether porosity reservoirs are filled from the bottom up (via a recharge well) or from the top down (via recharge ponds, ditches or French drain systems), the act of filling the reservoir tends to force entrapped air within the reservoir upward. That is, the same alluvial pore spaces that would otherwise be filled with water also contain air that is forced upward during the act of filling the porosity reservoir. The entrapped air cannot escape through the borders of the porosity reservoir since both the bottom aquiclude (e.g., bedrock layer) and the sidewalls are substantially impermeable. Similarly, the top surface of the porosity reservoir is typically covered by a layer of topsoil or similar overburden that is relatively impermeable to air movement. Thus, the entrapped air is forced upward during the reservoir filling process and increases in pressure as the air collects at the top of the reservoir. While natural water fluctuations in groundwater flow (i.e., through unconfined alluvial materials) are known to occur, the fluctuations in water level within a confined porosity storage reservoir occur much more quickly and are greater in magnitude than those that occur naturally.

Should excessive air pressure be allowed to build up in the alluvial materials during the recharge and extraction of water from porosity reservoirs, a cracking in the surface or separation of the native top soil from the alluvial material may occur, causing surface distress. This phenomenon is similar to bubbles being formed in a water bed when existing air is not allowed to escape as the mattress is filled with water. The net storage capacity of the porosity reservoir may be decreased if water cannot be stored all the way to the top soil-alluvial interface due to the presence of the entrapped air. Furthermore, an increase of air pressure within the alluvial pore spaces tends to decrease the injection rate of water into the porosity reservoir (i.e., gravity drainage of water is slowed due to the higher air pressure, and recharge wells must be run at a higher pressure to overcome the greater air pressure within the alluvial materials).

In addition to the above-described problems associated with entrapped air during the filling of the reservoir, the process of withdrawing water from the reservoir can cause the creation of a partial vacuum within the reservoir that inhibits or slows the further pumping of water from the reservoir. As with entrapped air, a vacuum created within the alluvial pore spaces of the reservoir is not easily filled due to the substantially impermeable borders of the porosity reservoir. Thus, extraction wells pump water with a reduced efficiently when a partial vacuum forms (i.e., as water is removed from the porosity reservoir).

It is with respect to these and other background considerations, limitations and problems that the present invention has evolved.

SUMMARY OF THE INVENTION

The present invention includes an underground porosity reservoir for storing water in alluvial deposits, wherein the reservoir is formed by one or more substantially water-impermeable barriers and an aquiclude that surround a volume of alluvial materials, so that water can be stored within the spaces or pores between the alluvial materials. A conduit is positioned below a surface layer of the reservoir so that an interior volume of the conduit communicates with the alluvial deposits of the reservoir (e.g., through an opening at the end of the conduit or through a series of perforations formed along the conduit). Additionally, an air vent is provided for connecting the interior volume of the conduit with air at substantially atmospheric pressure above the reservoir. Establishing communication between the underground conduit and the atmosphere above the reservoir allows air to pass to and from the reservoir during extraction and recharge operations, respectively. In particular, the atmospheric air within the interior volume of the conduit communicates with the pore spaces of the alluvial deposits within the reservoir to provide a path for (1) air entrapped within the pore spaces of the alluvial deposits to escape the reservoir as the reservoir is filled with water, and/or (2) air to enter the reservoir in order to substantially eliminate a partial vacuum formed within the pore spaces of the alluvial deposits as water is pumped from the reservoir.

In one preferred embodiment, an extraction and/or recharge well is used for pumping water out of (and into) the reservoir, and the conduit is positioned to run adjacent to the well. In a further embodiment, each conduit comprises a perforated pipe positioned just below the interface of the surface material (e.g., topsoil) and the alluvial deposits within the reservoir, and the perforated pipe is surrounded by coarse bedding material in order to maximize the transfer of air into and out of the conduit.

Another aspect of the present invention provides a method ventilating an underground porosity reservoir, wherein the reservoir is formed by one or more substantially water-impermeable barriers and an aquiclude, and water is stored within pore spaces of the alluvial material contained within the reservoir. The method includes the initial step of positioning a conduit below a surface layer of the reservoir so that an interior volume of the conduit communicates with the pore spaces of the reservoir. Next, air at substantially atmospheric pressure is provided to the interior volume of the conduit, such as by extending an air vent between the conduit and a region above the surface of the reservoir. In one embodiment, the method includes filling the reservoir with water so that air entrapped within the pore spaces of the alluvial material is forced upward and out of the reservoir through the conduit and the air vent. In a further embodiment, water is extracted from the reservoir so that a partial vacuum is formed within the pore spaces of the alluvial material as water is removed from the reservoir. Air within the conduit is then drawn into the reservoir to substantially eliminate the partial vacuum formed in the pore spaces of the alluvial material.

These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a typical river basin illustrating a perimeter of an underground porosity reservoir for use with an embodiment of the present invention.

FIG. 2 is a section view of the porosity reservoir taken substantially along the line 2-2 in FIG. 1, illustrating the details of an extraction/recharge well and a bedding configuration for an air ventilation conduit.

FIG. 3 is a section view of the porosity reservoir taken substantially along the line 3-3 in FIG. 1, illustrating the details of a vertical air vent providing atmospheric air to the air ventilation conduits shown in FIG. 2.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary underground reservoir system in accordance with the present invention. In particular, FIG. 1 illustrates a plan view of an exemplary river system or basin 20 comprising a riverbed 22 that flows along the top of alluvial deposits 24 (FIG. 2) formed within the boundary 26 of a floodplain that extends to either side of the current riverbed 22. An arrow 28 in FIG. 1 illustrates a direction of flow of the groundwater through the alluvial deposits 24. An underground porosity storage reservoir 30 is typically formed with a regular geometric boundary 32. FIG. 1 further illustrates the position of a plurality of extraction/recharge wells 40, air ventilation conduits 50, and air vents 60 within the porosity reservoir 30, as described in greater detail below. Additional details regarding the design, construction and technical aspects of underground reservoirs are disclosed within U.S. Pat. No. 6,840,710, incorporated by reference above.

FIG. 2 provides a section view of the underground reservoir 30 shown in FIG. 1 and illustrates that the reservoir is created by bounding a volume of alluvial deposits 24 with sidewalls 36 that follow the perimeter 32 shown in FIG. 1. The walls 36 are substantially water impermeable and are preferably vertical in orientation. In the embodiment shown, the walls 36 are bounded by an aquiclude 44 that extends below the floodplain boundary 26, although other materials and construction techniques may be used. The underground reservoir 30 encloses a volume of natural alluvium 24, and the water storage provided by the reservoir 30 is in the form of porosity storage within the pore spaces of the alluvial material (e.g., sand and gravel). Depending on the specific type of alluvial material, the usable water storage volume may range from 10% to 40% of the total enclosed volume of the reservoir 30. In an alternative embodiment, a different material, such as imported sand, gravel or recycled concrete, may be used in place of the natural alluvium 24.

In the embodiment shown in FIG. 2, a well 40 is utilized to withdraw the stored water from the porosity reservoir 30 during emptying operations. In another embodiment, the same well 40 may be utilized as a recharge well to help refill the porosity reservoir 30. In various embodiments one or more recharge wells may provide the sole means for filling the reservoir, while in other embodiments a series of surface features (e.g., recharge ditches or holding ponds) may be used in conjunction with (or instead of) the well 40 to provide top-down filling of the reservoir 30. Additionally, a French drain system buried near the topsoil-alluvial interface (as described in U.S. Pat. No. 6,840,710) may also be used to provide top-down gravity filling of the reservoir.

In order to alleviate the problems associated with entrapped air (i.e., during the filling of the porosity reservoir 30) and/or the formation of a vacuum within the reservoir (i.e., during extraction of water from the reservoir 30), the present invention provides for ventilating the pore spaces of the alluvial materials (e.g., to atmospheric pressure as described below). Ventilation of the porosity reservoir 30 provides pressure-relief during reservoir filling operations, and further provides a vacuum-break (i.e., allows for the introduction air within the pore spaces) as water is emptied from the reservoir 30.

In particular, one embodiment of the present invention utilizes one or more air ventilation conduits 50 (FIG. 1) that are arranged near the top of the alluvial material 24 within the porosity reservoir 30 (as shown in FIGS. 2 and 3). Each air ventilation conduit 50 preferably comprises a perforated pipe 52 (e.g., a PVC pipe) bedded within coarse gravel or a similar material. In one embodiment, each perforated pipe 52 is preferably wrapped in a geo-textile fabric to minimize the potential for clogging the pipe perforations. FIG. 2 illustrates that each pipe 52 is positioned within a trench 54 that is excavated through the topsoil layer 56 and into the uppermost region of the alluvial material 24. In one embodiment, a layer of the coarse bedding material 58 (e.g., gravel) is placed along the bottom of the trench 54, and the perforated pipe 52 is then positioned atop the bottom layer of bedding material 58. Additional bedding material 58 is then added to completely cover and surround the pipe 58. The remainder of the trench 54 is then preferably backfilled (e.g., with topsoil) as shown in FIG. 2.

While a perforated pipe 52 is illustrated as a preferred embodiment of air ventilation conduit 50 in FIG. 2, those skilled in the art will understand that alternative means for supplying an atmospheric interface at the appropriate depth within the reservoir (e.g., ditches or a series of vertical pipes) may be used in place of the perforated pipe 52. Thus, as noted below, the present invention is not limited to the use of perforated pipes 52 to ventilate an underground porosity storage reservoir.

In order to provide atmospheric pressure to each air ventilation conduit 50, one or more vertical air vents 60 are connected to each length of perforated pipe 52, as shown in FIG. 3. Each air vent 60 preferably comprises a non-perforated pipe (e.g., PVC pipe) having an interior volume and a first end that connects to the perforated pipe 52. A second end of the air vent 60 extends vertically through the topsoil layer 56 and terminates a predetermined distance above the top of the reservoir surface. A top end 62 of each air vent 60 is open to the atmosphere, and a conventional screen/deflection structure 64 is utilized to prevent precipitation, small animals, insects or other contaminants from entering the air vent 60. In the event that the air ventilation conduit 50 comprises means other than a perforated pipe 52, the air vent 60 similarly provides a path between such alternate means 50 and atmospheric air above the surface of the reservoir.

By connecting one end of the air vent 60 to a conduit 50, the interior volume of the air vent communicates with the interior volume of the conduit 50 (e.g., the perforated pipe 52). The air vents 60 thus provide atmospheric air to the air ventilation conduits 50, which in turn allow air to move into and out of the porosity reservoir 30. That is, the conduits 50 and air vents 60 provide a path for air to travel to and from the pore spaces of the alluvial material 24 during reservoir filling and emptying operations. Specifically, during a reservoir recharge operation, water typically travels downward through the pore spaces of the alluvial material 24 and forces entrapped air upward toward the top of the reservoir 30. This entrapped air enters the conduits 50 (e.g., through the perforations in the pipes 52) and travels along the conduit 50 until it exits the reservoir 30 through a vertical air vent 60. Similarly, during an extraction operation, a partial vacuum would normally be formed as water is removed from the pore spaces of the reservoir 30. The presence of atmospheric air within the conduits 50 allows air to travel downward through the pore spaces of the alluvial material 24 to take the place of the newly evacuated water and thereby prevent the formation of vacuum.

Thus, the provision of the air ventilation conduits 50 and vertical air vents 60 provide both a pressure-relief mechanism and a vacuum-break during recharge and extraction operations, respectively, within the porosity reservoir 30. In one embodiment, the position of the ventilation conduits 50 is selected so that a perforated pipe 52 runs adjacent to each well 40 to maximize both the vacuum-break and pressure-relief benefits of the present invention.

While FIGS. 1-3 illustrate one embodiment of the ventilation system of the present invention, those skilled in the art will recognize that alternative materials and configurations may be used to ventilate the porosity reservoir 30. For example, the precise depth of the air ventilation conduits 50 within the reservoir 30 may be varied to both ensure that the perforated pipes 52 are neither positioned too deep (i.e., to prevent the pipes from being flooded with water when the porosity reservoir 30 is at maximum capacity) nor too shallow (i.e., to ensure that the pipes 52 are surrounded by the porous alluvial material 24 as opposed to the substantially air-impermeable topsoil layer 56).

Additionally, while FIG. 1 shows an exemplary configuration of the extraction/recharge wells 40, air ventilation conduits 50, and vertical air vents 60, the present invention is not limited to any particular number or arrangement of these elements. Indeed, alternative embodiments of the present invention may connect each of the conduits 50 to take advantage of centrally located air vents 60 (i.e., reduce the overall number of vents). These vents could be located in designated areas where accidental damage is less likely, or where the appearance of the vents will not affect the overall aesthetic of the surface area above the porosity reservoir. In one embodiment, the vents 60 may be located in a building or “decoy structure” that further protects the vent from damage, insects and other contaminants. Alternatively, instead of comprising separate conduits attached to perforated pipes 52, the air vents 60 may comprise a non-perforated end of the perforated pipe 52 that is turned upward to extend above the surface level of the reservoir. As a further alternative, the ventilation conduit 50 and air vent 60 may be combined into a single pipeline having a lower portion (conduit 50) that extends into the alluvial deposits, and an upper portion (air vent 60) that extends above the top surface of the porosity reservoir 30. In this manner, the ventilation conduit 50 need only define at least one opening (e.g., at the end of the conduit) in lieu of a number of perforations extending along a length of the conduit.

It will be clear that the present invention is well adapted to attain the ends and advantages mentioned as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, various changes and modifications may be made which are well within the scope of the present invention. Thus, the various embodiments described above are provided by way of illustration only and should not be construed to limit the invention. Those skilled in the art will readily recognize various modifications and changes that may be made to the present invention without departing from the true spirit and scope of the present invention, which is set forth in the following claims. 

1. A method for ventilating an underground porosity reservoir, wherein the reservoir is formed by one or more substantially water-impermeable barriers and an aquiclude, and wherein water is stored within pore spaces of alluvial material contained within the reservoir, the method comprising: positioning a conduit below a surface layer of the reservoir, wherein the conduit includes at least one opening so that an interior volume of the conduit communicates with the pore spaces of the reservoir; and providing substantially atmospheric pressure to the interior volume of the conduit.
 2. The method according to claim 1, wherein the conduit comprises a perforated pipe.
 3. The method according to claim 2, wherein the step of positioning the perforated pipe below a surface layer of the reservoir further comprises: forming a trench through the surface layer and into the alluvial material; placing coarse bedding material within a bottom portion of the trench; positioning the perforated pipe atop the coarse bedding material; and filling the remaining portion of the trench with coarse bedding material and backfill material.
 4. The method according to claim 1, wherein the step of proving substantially atmospheric pressure to the interior volume of the conduit comprises: connecting a first end of an air vent to the conduit so that an interior volume of the air vent communicates with the interior volume of the conduit; and extending a second end of the air vent above a top surface of the reservoir to provide substantially atmospheric pressure to the interior volume of the air vent.
 5. The method according to claim 4, further comprising: filling the reservoir with water so that air entrapped within the pore spaces of the alluvial material is forced upward as water fills the reservoir; and allowing the entrapped air to enter the conduit from the pore spaces of the alluvial material and escape the reservoir through the air vent.
 6. The method according to claim 4, further comprising: extracting water from the reservoir so that a partial vacuum is formed within the pore spaces of the alluvial material as water is removed from the reservoir; and allowing air to enter the reservoir through the air vent and the conduit in order to substantially eliminate the partial vacuum formed in the pore spaces of the alluvial material.
 7. The method according to claim 4, further comprising: substantially enclosing the second end of the air vent to prevent contaminants from entering the air vent.
 8. The method according to claim 4, further comprising: positioning a plurality of conduits and attached air vents within the porosity reservoir.
 9. The method according to claim 1, further comprising: forming an extraction well that extends from the surface layer down to a bottom portion of the reservoir; and positioning the conduit to run adjacent to the extraction well.
 10. An underground porosity reservoir for storing water in alluvial deposits, the reservoir formed by one or more substantially water-impermeable barriers and an aquiclude, the reservoir including: a conduit positioned below a surface layer of the reservoir, wherein the conduit includes at least one opening so that an interior volume of the conduit communicates with the alluvial deposits of the reservoir; and means for providing substantially atmospheric pressure to the interior volume of the conduit.
 11. The porosity reservoir of claim 10, wherein the conduit comprises a perforated pipe.
 12. The porosity reservoir of claim 11, wherein: the perforated pipe is positioned within a trench that is formed through the surface layer and into the alluvial deposits of the reservoir; and a coarse bedding material surrounds the perforated pipe within the trench to enhance air transfer between the pore spaces of the alluvial deposits and the interior of the perforated pipe.
 13. The porosity reservoir of claim 10 wherein the alluvial deposits define pore spaces for storing water within the porosity reservoir, and wherein the interior volume of the conduit communicates with the pore spaces of the alluvial deposits within the reservoir.
 14. The porosity reservoir of claim 13, wherein the means for providing substantially atmospheric pressure to the interior volume of the conduit comprises an air vent having a first end connected to the conduit and a second end extending above a top surface of the reservoir so that an interior volume of the air vent communicates with the interior volume of the conduit and with atmospheric air above the reservoir.
 15. The porosity reservoir of claim 14 wherein: the reservoir includes a recharge well for filling the reservoir with water; and the conduit and air vent provide a path for air entrapped within the pore spaces of the alluvial deposits to escape the reservoir as the reservoir is filled with water.
 16. The porosity reservoir of claim 15 wherein the conduit is positioned to run adjacent to the recharge well.
 17. The porosity reservoir of claim 14 wherein: the reservoir includes an extraction well for pumping water out of the reservoir; and the air vent and conduit provide a path for air to enter the reservoir in order to substantially eliminate a partial vacuum formed within the pore spaces of the alluvial deposits as the water is pumped from the reservoir.
 18. The porosity reservoir of claim 17 wherein the conduit is positioned to run adjacent to the extraction well.
 19. The porosity reservoir of claim 14, further comprising a plurality of conduits and attached air vents positioned within the porosity reservoir. 